1. Field of the Invention
The present invention relates to a sheet finisher which can appropriately fold, sort, fasten and collect sheets which have come out of a copy machine and the like.
2. Description of the Prior Art
Japanese Patent Application Laid-Open No. 61-211272 (1986) discloses a previously proposed sheet finishing device.
This device is arranged to take the sheets which have come out of a copy machine, fold the same and then eject them onto an upper tray. Following this, the sheets on the upper tray are induced to engage a stopper and become aligned. They are then fastened together by stapling. After this fastening operation, the stopper is rotated and the fastened stack of sheets is collected by being dropped onto a lower tray. In this device the lower tray is arranged at a predetermined inclined or slanted angle.
However, with this prior art arrangement, as the stacks of sheets which are fastened together are induced to drop onto the lower tray under the influence of the stopper rotation only, the assuredness with which the sheets are unfailingly dropped into the intended position is low. That is to say, if the upper tray is formed of normal types of plastic, the effect of friction and static electrical charges hinders the sliding of the sheets.
In order to overcome the effect of the friction and static electricity, if the angle of the upper tray is overly increased, the capacity of the tray is undesirably reduced.
Further, if lower tray angle is fixed the capacity of the same is limited.
In particular, if a Z folding mode is selected, the folds of the Z folded sheet cause the thickness of the stack to become three times greater than normal. Depending on the number of stacks accumulated on the lower tray, the entry angle which is defined by a vertical line and the lower tray, rapidly becomes reduced.
Under these conditions, in the worst case, as the stack of sheets is dropped, the leading edge of the stack strikes against those already received in the tray and results in spillage.
Normally, with the so called Z sheet folding function, the sheets which are required to be folded in the folding device, are half folded and the half folded sheets are then again folded in half.
A prior art device which features this Z folding function is disclosed in Japanese Patent Application Laid-Open No. 61-217476 (1986).
In this arrangement a sheet folding transfer chute and a sheet transit chute having a pair of discharge rollers are provided at the downstream of an entrance deflector which is switched in accordance with the presence or absence of the demand for folding.
A first deflector is interposed at the downstream end of this sheet folding transfer chute, and first and second folding rollers which constitute a pair of folding rollers of a first folding stage and a folding position control guide chute are also provided.
Further, a second deflector is interposed downstream of the folding rollers of the first folding stage and second and third folding rollers which constitute a second folding stage roller pair and a second folding position control guide chute are provided.
Additionally, a third deflector is interposed downstream of the second folding stage roller pair, and third and fourth folding rollers which constitute a third folding stage roller pair and a third folding position control guide chute are provided.
Downstream of the roller pair of the third folding stage, a final guide chute is provided which merges with the above mentioned transit chute at its end.
A discharge roller is provided at the downstream of the final guide chute and the transit chute and arranged to discharge the treated sheets through an ejection opening onto a tray.
However, with this type of folding device when forming the folds in the sheets, as the sheet folding position control guide chute which receives the leading end of the sheet subjects the sheet to a degree of resistance, the bowing of the central portion of the sheet which is pinched by the folding rollers is reduced, and in addition to this during the half and Z folding modes, for example, depending on the size of the sheet, first to third sets of folding rollers are necessary in addition to the sheet folding position control guide chute. Accordingly, the construction of the finisher becomes complex, expensive and cannot be rendered compact.
Further, as the discharge rollers and the tray are fixed in place, it is not possible for example, to continuously Z fold a large number of sheets. That is to say, as the thickness of the folded and unfolded ends of the Z folded sheets is notably different, as the number of sheets increases the upper surface of the stacked sheets rapidly becomes inclined with respect to the surface of the tray.
Under these conditions the accumulative capacity of the device is lowered and the manner in which the sheets are discharged and pushed out onto the tray deteriorates the stacking neatness.
Further, the sheet folding mechanism is required to include a half folding mode which folds the sheets in half, a Z folding mode which folds the sheets and then folds the folded section again, in addition to a non-folding mode.
With this above mentioned prior art arrangement irrespective of the sheet folding mode the sheet which have been processed are discharged at a predetermined height above the tray. As the thickness of the folded sheets is two to three times that of the non-folded ones, in order to increase the accumulative capacity, it has been proposed to increase the distance between the top of the tray and the sheet discharge means.
However, this measure leads to the problem that, particularly during the non folding mode, the mass per unit area of the sheet is relatively small and the neatness with which the sheets are stacked is reduced. That is to say, the layer of air between the sheet being discharged and the surface onto which the sheet is intended to drop, produces a floating effect which deteriorates the neatness with which the sheets pile one on the other.
Normally, sheet finishers are provided with a fastening device which staples the collected stack of sheets together. While this appears to be desirable at first glance, before the sheets can be appropriately stapled they must have their side and top edges aligned.
In order to achieve this alignment or setting, one prior proposed arrangement has provided the tray with two side edges and base section and has utilizes the weight of the sheet in combination therewith to define means for suitably aligning the sheets in a suitably neat manner.
An alternative arrangement has provided one fixed side edge, a base and has added an adjustable guide which pushed sideways toward the single fixed edge in order to improve the neatness of the sheet stack.
However, the former arrangement is such that as the width of the guide is fixed, and cannot be reduced to exactly that of the sheets in order to permit the same to received without incident, the desired effect has not been achieved. With the latter arrangement in order to adjust the width of the guide, a drive mechanism is necessary. This provision increases the bulk of the arrangement undesirably and further does not permit the mixing of different sheet sizes.
In connection with the fastening devices which staple the stack of sheets together, the stapler must be moved to a fastening position for the stapling operation and then back to its home or original position after the stapling is completed. An example of a mechanism for returning the stapler to its original or home position can be found in Japanese Patent Application Laid-Open No. 59-69346 (1984). However, with this type of prior art arrangement the stapler must be moved a relatively large distance from its home position to its fastening one. As a result the layout of the finisher is rendered undesirably wide and prevents the achievement of a desirably compact arrangement.
A further problem comes in that the large distance through which the stapler must be moved requires a finite amount of time and slows the overall operation of the finisher.